The present invention generally relates to refrigeration apparatus, and more particularly the invention is concerned with a refrigeration apparatus receiving relatively reduced amounts of electrical energy and having control means for most efficiently utilizing the energy received by the refrigeration apparatus.
The invention is useful for practically any type of electrical refrigeration apparatus, but it is of greatest importance in battery driven refrigerators. The following the invention will mainly be described in connection with refrigeration apparatus driven by rechargeable batteries, especially 12 volt or 24 volt batteries. It is, however, to be understood that the invention is not restricted to this type of power source and that the invention can also be used for any electrically-operated refrigeration apparatus.
In vehicles and boats the supply of electric energy is very different if the motor is running and if the motor is not running, that is if the generator is recharging the batteries or not. In automobiles and most important in boats there is often a need of large amounts of electric energy for lighting, heating, refrigeration purposes etc. at times when the motor is not running. For offering a sufficient amount of electric energy attempts have been made to give the cars and the boats increased battery capacity, often a bank of several batteries, and stronger and stronger generators. Because of the restricted ability of the batteries to become recharged this has not been an ideal solution of the problem, and in order to obtain a sufficient recharging of the battery or the batteries it has often been necessary to run the motor for a longer period than would otherwise have been necessary.
Attempts have been made to reduce the current consumption of certain electric apparatus. In this connection refrigeration apparatus provide special problems since the refrigeration needs often exceed the avaliable electric capacity. The problems may partly be solved in that the refrigeration apparatus is used to a greater extent when the supply of current is good, that is when the motor is running, than when the motor is not running. By lowering the temperature of the refrigerated space to a level beyond the normal cooling level some stored cooling capacity is obtained, and therefore the time between calls for more cooling from the thermostat is prolounged. For increasing the stored cooling capacity some refrigeration apparatus included with a so called eutectic cooler plate which is mounted in the refrigerated space instead of the conventional cooler coils.
The eutectic cooler plate is a closed body containing a spirit or salt solution having a very low freezing temperature, for instance -15.degree. to -20.degree. C. By connecting the refrigeration apparatus while the motor is operating, so that the eutectic cooling plate obtains such very low temperature, such an amount of accumulated cooling energy is obtained that the eutectic plate normally maintains the coolness of the refrigerated space for many hours even if the motor is not running, for instance as long as 15-20 hours.